Method of modifying a boat hull to obtain enhanced lift and rough water stability

ABSTRACT

Hydrofoil craft, particularly a method of economically modifying a conventional hull by means of foils to obtain enhanced lift and rough water stability. The method is characterized by defining an axial tunnel(s) intermediate the bow and transom of a catamaran hull or V-bottom hull modified with chine mounted aerofoils; positioning a flexible dihedral foil beneath the water line and on either side of the bow so as to obstruct and create a turbulence in the forward end of the tunnel, while cushioning shock and lifting the bow; and simultaneously enclosing the transom end of the tunnel with a foil, so as to compress the turbulence and lift the transom.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Hydrofoil craft, particularly the use of flexible foils to obtain a veryhigh ratio of speed to horsepower, by enhancing lift and stability inrough water.

2. Description of the Prior Art

WRAY, U.S. Pat. No. 3,357,390

LO BUE, U.S. Pat. No. 3,372,663

COLES, U.S. Pat. No. 3,604,384

DANAHY, U.S. Pat. No. 3,763,811

HOPPE, U.S. Pat. No. 4,606,291

APRIL, U.S. Pat. No. 4,649,851

GERDSEN et al., U.S. Pat. No. 4,665,853

STEINBERG, U.S. Pat. No. 4,715,304

SUMMARY OF THE INVENTION

A method of modifying a boat hull to obtain enhanced lift and roughwater stability. The method includes defining or modifying with chineaerofoil skirts an axial tunnel(s) intermediate the bow and transom ofthe boat hull, positioning flexible dihedral foils below the water lineand on the bow so as to obstruct and create turbulence in the forwardend of the tunnel while cushioning and lifting the bow. Simultaneously,the transom end of the tunnel is enclosed with stern foils so as tocompress said turbulence and thereby lift the transom.

Particularly a hydrofoil system for modifying a hull in order to obtainexcellent stability and performance at high speeds in rough waterresulting from substantial hull lift, viz:

1. Hydrodynamic lift from the twin swept back, surface piercing,flexible forward hydrofoils.

2. Hydrodynamic lift from the tunnel(s) on a catamaran hull or a Vbottom hull modified with chine mounted aerofoils and stern foil(s) bycompressing the flow of dense spray at high velocity with the sternfoil(s).

3. High pressure and lift in the tunnel and on the chine and/or sternfoils from dense spray at high velocity with the transom end of thetunnel(s) restricted by the stern foil(s).

The substantial hull lift generated by the foil system reduces the roughwater wave profile impacted by the hull, so as to reduce wave shock andimprove hull stability and performance at high speeds.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a catamaran hull modified accordingto the present invention.

FIG. 2 is a rear elevation thereof.

FIG. 3 is a front elevation.

FIG. 4 is an enlarged fragmentary front elevation, partially in sectionshowing the fitting of twin flexible foils 40, 47 adjacent the bow of aboat.

FIG. 5 is a fragmentary rear elevation, showing a stern foil hovercrafttype skirt.

FIG. 6 is a fragmentary side elevation, showing a stern foil hovercraftskirt, pivoted on the transom and as shown in FIG. 5.

FIG. 7 is a rear elevation of a twin tunnel hull construction having asingle rear engine.

FIG. 8 is a similar rear elevation of a twin tunnel hull constructionhaving dual rear engines.

FIG. 9 is a showing of a modified twin tunnel construction having asingle rear engine.

FIG. 10 is a showing of a hull having a single tunnel with twin engines.

FIG. 11 is a side elevation, partially in phantom, showing the catamaranhull of FIGS. 1 and 2 embodying pairs of forward and stern twin foils.

FIG. 12 is a fragmentary enlarged section showing fitting of the pairsof foils adjacent the bow and stern to intersect the tunnels.

FIG. 13 is a longitudinal section of the boat illustrated in FIG. 11 andshowing the boat underway at low speed.

FIG. 14 is a similar longitudinal view showing the FIGS. 11 and 13 hullunderway at high speed with the transom 32 closed, so as to compress theturbulence within tunnel 26.

FIG. 15 is a rear elevation of the boat illustrated in FIG. 15.

FIG. 16 is a schematic exploded view of the boat shown in FIGS. 11, 13and 14, and illustrating the action of the pairs of forward foils andthe rear transom foil. The turbulence and dense spray created by thepair of forward foils and the compression of this turbulence in thetunnels and by the transom foils enclosing the tunnels, is indicated byincreasing bubble density aft.

FIG. 17 is a fragmentary side elevation of a flexible forward foil.

FIG. 18 is a bottom plan of the foil illustrated in FIG. 17.

FIG. 19 is a fragmentary end elevation illustrating placement of aforward foil on a V-bottom boat.

FIG. 20 is a schematic illustration of the use of shims or hydraulicmeans to adjust the θ [theta] angle of attack of the forward foil.

FIG. 21 is a side elevation of a twin tunnel hull having forward foilsand a pair of stern transom foils.

FIG. 22 is a plan thereof.

FIG. 23 is a side elevation of a V-bottom hull modified with a chineaerofoil skirt 112 to define axial tunnels interrupted by the forwardfoils and the rear transom foils 118.

FIG. 24 is a rear elevation.

FIG. 25 is a plan of the V-bottom hull illustrated in FIGS. 23 and 24.

FIG. 26 is a fragmentary enlarged side elevation of the V-bottom hullillustrated in FIGS. 23 and 24 and showing compression of the tunnelturbulence and dense spray by means of rear foils 118.

FIG. 27 is a rear elevation of the boat illustrated in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention may be directed to a catamaran form of hull readilyfabricated from metal or moldable plastic material and modified toincluding a tunnel(s) defined between two hull sections or pontoons orcreated on a V-bottom hull with chine and pairs of foils fore-and-aftadapted to be acted upon both by water and by air in order to assist inlifting the hull when the boat is under power. The forward foils on thebow of the boat are formed as surface piercing hydrofoils and so shapedthat they cooperate in creating turbulence, spray and waves in thestream passing through the tunnel while assisting in increasing theflotation lift of the hull which is largely out of the water when theboat is traveling at high speeds. A combination of lift foils isprovided by the forward surface piercing hydrofoils, the tunnel as asurface effects hull and the rear or transom foils in the form of ahovercraft skirt.

FIGS. 1, 2, 3, and 11, show a catamaran hull indicated generally at 20and having integral port and starboard pontoons 22 and 24 respectively.Hull 20 may be fabricated from metal or molded integrally of a plasticmaterial already well known for boat hull purposes, such aspolyurethane. Regardless of the mode of construction, the pontoons 22,24 define between them an axial tunnel 26, including a lift surface 28,cooperatively associated with pairs of fore flexible foils indicatedgenerally at 30, 31 and a pair of stern or transom foils 32, 33. Theform, function and mode of operation of the foil pairs 30, 31 and 32, 33are explained below.

Hull 20 further includes open cockpit 34, furnished with windshield 36.At the rear, cockpit 34 is closed by a transom 38 appropriatelyreinforced to support an outboard motor 39 or, alternatively, an inboardor outboard drive which may be of reasonably small power for the speedswhich are attained in rough water. For example, with a 235 horsepowermotor, a 23 foot boat modified in accordance with the present inventionhas been propelled relatively smoothly in 5 foot waves at a speed ofapproximately 50 miles per hour. As shown in all views, forward port andstarboard foil pairs 30, 31 are separately attached with bolts to therespective outside pontoon surfaces. Similarly, separate aft port andstarboard foils 32 and 33 are individually secured to the hull.

As shown in FIG. 4, the starboard dihedral foil assembly 31 may comprisemain cantilevered flexible foil 40, rubber shock pad 41 to reduce shockand fatigue of the metal foil, reinforcing 42 in the starboard pontoon,a bolt plate 43, and a bolt and lock nut 44. In addition, the starboardfoil assembly 31 may comprise a channel 45, rubber shock pad 46, a lowercantilevered flexible foil 47, rubber shock 46, a fence 48 for addeddirectional stability and seating of bolt and lock nut 49. The boltsallow the entire foil assembly or only the lower foil 47 and fence 48 tobe easily removed for replacement or repair. Foils 40, 47 which bend intorsion may be replaced with larger or smaller foils depending onrequirements for higher speed or rough water operations.

FIG. 5 shows stern or transom foil 32 which can be raised or lowered byhydraulic or pneumatic ram or rams 50. When the boat is traveling athigh speeds into surface winds, the combined air and spray are dense andhave a large velocity through the tunnel when aft foil 32 in the form ofa hovercraft skirt is raised. When foil 32 is lowered, the density ofthe spray is increased, generating increased pressure and lift withintunnel 26, on lift surface 28 and on the pair of transom foils 32 and33. As illustrated in FIG. 5, transom foils 32 and 33 are attached tohull 22 and 24 with gasket 51 held in place with clamp 52 to prevent airescaping between foil 32 and hull 22. Increased hull lift by loweringstern foil 32 reduces shock when hull 22 is going into the wind in roughwater, having an increased wave frequency and profile. The design at thestern foil tends to prevent the bottom of the foil from being liftedabove the surface of the water and cause the propeller(s) to cavitate.

FIG. 7 shows rear foils 32 and 33 mounted on a twin tunnel hull poweredby single engine 39. FIG. 8 shows foils 32 and 33 mounted on a twintunnel hull powered by two engines 38, 39, and FIG. 10 shows a singlefoil 32 mounted on a single tunnel hull with two engines. FIG. 9 showsfoils 32 and 33 mounted on a twin tunnel hull with a single engine.

As illustrated in FIGS. 13 to 16, the bow foils 30, 31 and transom foils32, 33 cooperate with tunnel 26 to provide lift to the hull, accordingto the surface effects principle and in a manner which is not completelyunderstood. It is theorized, however, that a part of the lift is derivedfrom the action of the water and to a lesser degree the action of theair upon the forward surfaces of the pontoons 22 and 24. The water andthe air combine to form a dense spray which also exerts an upward forceon the foils themselves, i.e., forward hydrofoils 30, 31 and on thehovercraft type rear foils 32, 33. In addition, water and dense spray inthe form of turbulence created by the forward foils exert upward forcesin the tunnel especially upon the relatively large horizontal liftsurfaces in accordance with the surface effects principle. In addition,when the boat is in the position of FIG. 14 while being operated at highspeed, dense spray and waves are compressed in the rearward portion ofthe tunnel and not only exert an upward force directly, but alsoindirectly. The water, dense spray and foam, at large velocity beingcompressed by motion of the boat between the walls of the tunnel in therear of the tunnel and on the rear foils, exert considerable lift.

In FIG. 17, there is illustrated the construction of a flexible forwardfoil 60 which is mounted upon I-beam 62 and includes a curvate, sweptback configuration such that the foil passes over debris without damageand bends in torsion so as to reduce fatigue from bending. The leadingedge 64 of I-beam 62 is inclined downwardly and aft, so as to reducedrag and a shock pad 66 may be fitted intermediate the I-beam 62 and thehull exterior 74 prior to fastening with through bolts 68, 70 and 72.Similarly shock pad 80 may be secured intermediate I-beam 62 and thefoil 60 by means of through holes 76, 78.

FIG. 19 illustrates the placement of a forward foil 86 on a V-bottomhull by means of I-beam 84 and includes angle fence 88.

FIG. 20 is a schematic side view designating theta (θ) as the angle ofattack of forward foil which may be adjustable by means of shims orhydraulic controls (not illustrated).

FIGS. 21, 22 and 27 detail a single tunnel 96 construction, having bowmounted foils 94, transom foils 102 104 hydraulically actuated by struts106, 108. Hovercraft type skirts 98, 100 may be employed, also, toenclose the transom end of the tunnel 96.

As illustrated in FIGS. 23-26, in addition to the forward foils 122mounted beneath the V-bottom hull 110, it is possible to obtain evengreater lift and stability from dense spray by the use of winglikelongitudinal chine mounted aerofoils 112 mounted between the chine andskeg of the hull from midsection to the stern to generate two tunnels tocooperate with the already described foils and hull surfaces. As in theabove-described constructions, transom foils 118 may be actuated byhydraulic cylinder 116.

I claim:
 1. Method of modifying a powered boat hull to obtain enhancedlift and rough water stability, comprising:(a) defining at least oneaxial tunnel extending from the bow to the transom of the boat hull; (b)positioning a pair of flexible foils on each side of the bow and beneaththe water line and boat hull so as to obstruct and create turbulence ofdense spray in the forward end of the tunnel, while cushioning shock andlifting the bow; and (c) simultaneously peripherally enclosing thetransom end of the tunnel with a foil forming a skirt extendingsubstantially across said tunnel, so as to prevent air escaping and tocompress said turbulence and thereby lift said transom.
 2. Method ofmodifying a powered boat hull to obtain enhanced lift and rough waterstability as in claim 1, including varying said enclosing the transomend, so as to control the amount of lift of said hull.
 3. Method ofmodifying a powered boat hull to obtain enhanced lift and rough waterstability as in claim 2, wherein said hull is a catamaran.
 4. Method ofmodifying a powered boat hull to obtain enhanced lift and rough waterstability as in claim 2, wherein said hull is a V-hull.
 5. Method ofmodifying a powered boat hull to obtain enhanced lift and rough waterstability as in claim 4, including enclosing the sides of said tunnelfore and aft by extending a chine aerofoil skirt on either side of saidhull from the point of attachment of said foils to the transom. 6.Method of modifying a powered boat hull to obtain enhanced lift andrough water stability, comprising:(a) defining twin axial tunnelsintermediate the bow and transom of the hull; (b) positioning a pair offlexible foils on each side of the bow and beneath the water line andboat hull so as to obstruct and create turbulence of dense spray in theforward end of each tunnel, while cushioning shock and lifting the bow;and (c) simultaneously peripherally enclosing the transom end of eachtunnel with a foil forming a skirt extending substantially across itsrespective tunnel, so as to prevent air escaping and to compress saidturbulence of dense spray and lift said transom.